Endogenous atrial natriuretic peptides (ANP), also called atrial natriuretic factors (ANF) have diuretic, natriuretic and vasorelaxant functions in mammals. The natural ANF peptides are metabolically inactivated, in particular by a degrading enzyme which has been recognized to correspond to the enzyme neutral endopeptidase EC 3.4.24.11, also responsible for e.g. the metabolic inactivation of enkephalins.
Neutral endopeptidase (also known as NEP, endopeptidase 24.11, EC 3.4.24.11; neprilysin, enkephalinase; atriopeptidase; fibroblast metalloelastase, kidney-brush-border neutral peptidase, membrane metallopeptidase A, MME g.p. (homo sapiens), common acute lymphocytic leukemia antigen (CALLA) or CD antigen (CD10)) is a zinc-containing metalloprotease found in many organs and tissues including brain, kidneys, lungs, gastrointestinal tract, heart and peripheral vasculature. NEP cleaves a variety of peptide substrates on the amino side of hydrophobic residues [see Pharmacol Rev, Vol. 45, p. 87 (1993)]. Substrates for this enzyme include, but are not limited to, atrial natriuretic peptide, brain natriuretic peptide (BNP), met- and leu-enkephalin, bradykinin, neurokinin A, endothelin-1, angiotensins, adrenomedullin, glucagon-like peptides, glucagon, insulin B chain, amyloid betas and substance P. Some of these peptides have potent vasodilatory and neurohormone functions, diuretic and natriuretic activity or mediate behaviour effects. ANP is a potent vasorelaxant and natriuretic agent [see J Hypertens, Vol. 19, p. 1923 (2001)]. Infusion of ANP in normal subjects resulted in a reproducible, marked enhancement of natriuresis and diuresis, including increases in fractional excretion of sodium, urinary flow rate and glomerular filtration rate [see J Clin Pharmacol, Vol. 27, p. 927 (1987)]. However, ANP has a short half-life in circulation, and NEP in kidney cortex membranes has been shown to be the major enzyme responsible for degrading this peptide [see Peptides, Vol. 9, p. 173 (1988)]. Thus, neutral endopeptidase inhibitors should increase plasma levels of ANP and, hence, are expected to induce natriuretic and diuretic effects.
Furthermore, NEP enzyme plays an important role in blood pressure homeostasis and cardiovascular health.
Neprilysin and other proteases such as insulin-degrading enzyme (IDE), endothelin-converting enzyme (ECE), and NEP-2 are important degrading enzymes of amyloid-β peptide (Aβ) in the central nervous system (CNS) (Bart De Strooper et al. 2010, Physiol. Rev. 90:465-494; Nobuhisa Iwata et al. 2001, Science, Vol. 292, 1550-1552, Julie A. Carson et al. 2002, Journal of Neurochemistry. 2002, 81, 1-8). Decreased clearance of CNS A has been suggested to be linked to the development of neurodegeneration such as Alzheimer's disease (Kwasi G. Mawuenyega et al. 2010, Science, Vol. 330, 1774). Consequently, NEP inhibitor compounds that access critical CNS regions might inhibit CNS NEP and increase CNS Aβ peptide level.
Although the impact of pharmacologic NEP inhibition on CNS Aβ level and cognition in humans is unknown and there is no clinical indication that inhibiting NEP would be associated with cognitive impairment, NEP inhibitors displaying a beneficial peripheral inhibitory effect with minimized inhibitory CNS effect may be advantageous and may potentially offer an added level of safety.